Complex reaction kinetics of a Mannich reaction in droplets under electrospray conditions

Zühlke, Martin; Koenig, Justin; Prüfert, Chris; Sass, Stephan; Beitz, Toralf; Löhmannsröben, Hans‐Gerd; Thoben, Christian; Zimmermann, Stefan; Urban, Raphael D.; Abel, Bernd

doi:10.1039/d2cp05392f

“…The described observations indicate that the postulated partial solvation has a significant impeding effect on the cation-cation reaction of 2 b + and 6 + leading to 7 b + , although the Mannich reaction is, in general, promoted by the environment of charged microdroplets (demonstrated in the literature [4,40] and shown above for diketone 2 a). In contrast, the cation-cation reaction between 4 b + and 2 b + is apparently promoted by the microdroplet environment.…”

Section: Methodsmentioning

confidence: 57%

Control of Intermediates and Products by Combining Droplet Reactions and Ion Soft‐Landing

Yang,

Urban,

Lorenz

et al. 2023

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Despite being recognized primarily as an analytical technique, mass spectrometry also has a large potential as a synthetic tool, enabling access to advanced synthetic routes by reactions in charged microdroplets or ionic thin layers. Such reactions are special and proceed primarily at surfaces of droplets and thin layers. Partial solvation of the reactants is usually considered to play an important role for reducing the activation barrier, but many mechanistic details still need to be clarified. In our study, we showcase the synergy between two sequentially applied "preparative mass spectrometry" methods: initiating accelerated reactions within microdroplets during electrospray ionization to generate gaseous ionic intermediates in high abundance, which are subsequently mass‐selected and soft‐landed to react with a provided reagent on a substrate. This allows the generation of products at a nanomolar scale, amenable to further characterization. In this proof‐of‐concept study, the contrasting reaction pathways between intrinsically neutral and pre‐charged reagents, respectively, both in microdroplets and in layers generated by ion soft‐landing are investigated. This provides new insights into the role of partially solvated reagents at microdroplet surfaces for increased reaction rates. Additionally, further insights into reactions of ions of the same polarity under various conditions is obtained.

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“…[39] Reaktionen, die an der Tröpfchenoberfläche ablaufen, können als "Zwischensituation" betrachtet werden und erfahren eine Beschleunigung im Vergleich zur Reaktion im Inneren des Tröpfchens (Abbildung 3A). Die Situation kann sich entscheidend ändern, wenn die Reaktanten geladene Gruppen Die geschilderten Beobachtungen deuten darauf hin, dass die postulierte partielle Solvatisierung die Kation-Kation-Reaktion von 2 b + und 6 + , die zu 7 b + führt, erheblich hemmt, obwohl die Mannich-Reaktion im Allgemeinen durch die Umgebung geladener Mikrotröpfchen begünstigt wird, wie in der Literatur nachgewiesen [4,40] ) auf geerdeten leitfähigen Oberflächen nachgewiesen. [12] Wenn sich die Ionen beim Kontakt mit der Oberfläche aufgrund einer dünnen isolierenden Schicht nicht entladen, lädt sich die Substratoberfläche entgegengesetzt zu den abgeschiedenen Ionen auf, so dass sich die Ladung an der Grenzfläche ausgleicht (Details zum Konzept der Bildladung und zum Zwei-Platten-Kondensator-Modell wurden bereits früher berichtet [21,41,42] ).…”

Section: Ergebnisse Und Diskussionunclassified

“…Die geschilderten Beobachtungen deuten darauf hin, dass die postulierte partielle Solvatisierung die Kation‐Kation‐Reaktion von 2 b + und 6 + , die zu 7 b + führt, erheblich hemmt, obwohl die Mannich‐Reaktion im Allgemeinen durch die Umgebung geladener Mikrotröpfchen begünstigt wird, wie in der Literatur nachgewiesen [4,40] und oben für das Diketon 2 a gezeigt wurde. Im Gegensatz dazu wird die Kation‐Kation‐Reaktion zwischen 4 b + und 2 b + offenbar durch die Umgebung der Mikrotröpfchen begünstigt.…”

Section: Ergebnisse Und Diskussionunclassified

Kontrolle von Intermediaten und Endprodukten durch Kombination von Tröpfchenreaktionen und “Ion Soft‐landing”

Yang,

Urban,

Lorenz

et al. 2023

Angewandte Chemie

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Despite being recognized primarily as an analytical technique, mass spectrometry also has a large potential as a synthetic tool, enabling access to advanced synthetic routes by reactions in charged microdroplets or ionic thin layers. Such reactions are special and proceed primarily at surfaces of droplets and thin layers. Partial solvation of the reactants is usually considered to play an important role for reducing the activation barrier, but many mechanistic details still need to be clarified. In our study, we showcase the synergy between two sequentially applied "preparative mass spectrometry" methods: initiating accelerated reactions within microdroplets during electrospray ionization to generate gaseous ionic intermediates in high abundance, which are subsequently mass‐selected and soft‐landed to react with a provided reagent on a substrate. This allows the generation of products at a nanomolar scale, amenable to further characterization. In this proof‐of‐concept study, the contrasting reaction pathways between intrinsically neutral and pre‐charged reagents, respectively, both in microdroplets and in layers generated by ion soft‐landing are investigated. This provides new insights into the role of partially solvated reagents at microdroplet surfaces for increased reaction rates. Additionally, further insights into reactions of ions of the same polarity under various conditions is obtained.

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Chemical Kinetics in Microdroplets

Wilson,

Prophet

2024

Annual Review of Physical Chemistry

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Micrometer-sized compartments play significant roles in driving heterogeneous transformations within atmospheric and biochemical systems as well as providing vehicles for drug delivery and novel reaction environments for the synthesis of industrial chemicals. Many reports now indicate that reaction kinetics are accelerated under microconfinement, for example, in sprays, thin films, droplets, aerosols, and emulsions. These observations are dramatic, posing a challenge to our understanding of chemical reaction mechanisms with potentially significant practical consequences for predicting the complex chemistry in natural systems. Here we introduce the idea of kinetic confinement, which is intended to provide a conceptual backdrop for understanding when and why microdroplet reaction kinetics differ from their macroscale analogs. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 75 is April 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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Complex reaction kinetics of a Mannich reaction in droplets under electrospray conditions

Abstract: The solution of a Mannich reaction was electrosprayed to study their conversion ratio at various ES parameter. Implementing new methods demonstrated low influence of the gas phase and a high effect of the life time and the charge of the μ-droplets.

Cited by 3 publications

References 92 publications

Control of Intermediates and Products by Combining Droplet Reactions and Ion Soft‐Landing

Control of Intermediates and Products by Combining Droplet Reactions and Ion Soft‐Landing

Kontrolle von Intermediaten und Endprodukten durch Kombination von Tröpfchenreaktionen und “Ion Soft‐landing”

Chemical Kinetics in Microdroplets

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